Referring to FIG. 18 showing a schematic diagram of image artifact associated with the prior art, an image comprises 5×5 pixel blocks, a bold straight line indicates an edge of the image, and the image is located at the right side of the bold straight line L. Although the image theoretically includes image blocks at the right side of the bold straight line L, since the pixels blocks are already in a smallest unit possible, the image edge L perceived by the human eye cannot be more accurately presented than as shown in FIG. 18, in which the edge of the image is illustrated by a plurality of dotted pixel blocks. However, such image processing results in obvious image artifact when actually perceived by the human eye; that is, the human eye in fact sees a jagged edge instead of a smooth, straight line. In a conventional solution for overcoming the image artifact, a pixel value of a particular pixel block is determined by oversampling the pixel block located at an edge of an image. For example, the pixel block is divided into a plurality of sub-blocks, and the pixel value of the pixel block is then determined after calculating the number of sub-blocks that belong to the image. Yet, the oversampling technique requires substantial and complicated mathematical computations and associated logic operations that inevitably impose excessive burdens on an overall image system. Particularly for a real-time image processing system, the oversampling technique can be undesirable. Therefore, a solution for overcoming the drawbacks of image artifact associated with the prior art is in need.